Composite diamond compacts

ABSTRACT

A composite diamond compact is provided which has a diamond compact ( 12 ) bonded to a cemented carbide substrate ( 10 ). The composite diamond compact is characterised by the second phase for the diamond compact ( 12 ) and the binder for the cemented carbide substrate ( 10 ) both being a nickel/cobalt alloy.

BACKGROUND OF THE INVENTION

This invention relates to composite diamond compacts.

Diamond compacts, also known as polycrystalline diamond or PCD, are wellknown in the art and are used extensively in cutting, milling, drillingand other abrasive operations. Diamond compacts are polycrystalline innature and contain a high diamond content. Diamond compacts may beproduced without the use of a second or bonding phase, but generallycontain such a phase. When such a phase is present, the dominantcomponent of the phase is generally a diamond catalyst/solvent such ascobalt, nickel or iron or a combination thereof.

Diamond compacts are manufactured under elevated temperature andpressure conditions, i.e. conditions similar to those which are used forthe synthesis of diamond.

Diamond compacts tend to be brittle and so in use they are usuallybonded to a substrate, the substrate generally being a cemented carbidesubstrate. Bonding of the diamond compact to the substrate willgenerally take place during the manufacture of the compact itself.Diamond compacts bonded to a substrate are known as composite diamondcompacts.

Composite diamond compacts are used in a variety of applications and, inparticular, in drilling applications. The bonding phase for suchcomposite diamond compacts is generally cobalt. Cobalt undergoes a phasetransformation at temperatures above about 400° C. This gives rise toproblems in the use of composite diamond compacts in drillingapplications where temperatures of the order of 700° C. or higher areencountered at the cutting edge of such compacts. The phasetransformation of the cobalt at these temperatures results in thermalfatigue craze cracking and snake skin cracking of the composite compactsduring drilling applications.

SUMMARY OF THE INVENTION

According to the present invention, a composite diamond compactcomprises a diamond compact bonded to a cemented carbide substrate, thediamond compact comprising a polycrystalline bonded mass of diamondcrystals present in an amount of at least 80 percent by volume of thecompact and a second phase consisting essentially of a nickel/cobaltalloy, and the cemented carbide substrate comprising a mass of carbideparticles bonded into a coherent form by means of a binder consistingessentially of a nickel/cobalt alloy.

Further according to the invention, there is provided the use of acomposite diamond compact as described above in the abrasiveapplications where temperatures in excess of 500° C. are encountered ata cutting edge provided on the compact.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a sectional side view of an embodiment of a compositediamond compact of the invention.

DESCRIPTION OF EMBODIMENTS

The composite diamond compact of the invention is characterised by thealloy which is present in the diamond compact and in the cementedcarbide substrate. The alloy in both layers consists essentially of anickel/cobalt alloy. This means that the components of the alloy willconsist essentially of nickel and cobalt with other components beingpresent in trace or minor amounts only. It has been found that acomposite diamond compact of this nature has a significantly lowertendency to failure through delamination than prior art compositediamond compacts. Braze delamination occurs when composite abrasivecompacts are brazed into drill bits. The typical braze alloys used arezinc containing alloys. Zinc corrosion attack of cobalt binder in thesubstrate together with residual stresses in the substrate causesdelamination cracking during the bit brazing process. Further, thepresence of nickel increases significantly the thermal fatigueresistance of the compact and reduces the tendency for snake skincracking to occur during operations such as drilling where temperaturesof the order of 700° C. or higher are encountered.

Thus, the invention also provides the use of a composite abrasivecompact in abrasive applications where temperatures in excess of 500° C.are encountered at a cutting edge of the compact. The cutting edge willgenerally be provided by the peripheral edge of the diamond compact. Theabrasive applications may be cutting, drilling, milling or the like.

A mass ratio of nickel to cobalt in the alloy will generally range from75:25 to 20:80 and preferably in the range 30:70 to 45:55. A typicalexample of an alloy is one containing a mass ratio of nickel to cobaltof 40:60. The carbide particles of the substrate may be tungsten carbideparticles, tantalum carbide particles, titanium carbide particles,molybdenum carbide particles or a mixture containing two or more of suchparticles.

The composite diamond compact of the invention may be made by methodsknown in the art. More particularly, a mass of diamond particles may beplaced on a surface of a cemented carbide substrate forming an unbondedassembly which is then subjected to diamond synthesis conditions. Thealloy from the substrate infiltrates the diamond mass forming a diamondcompact which bonds to the substrate. In one preferred form of theinvention, a recess is formed in the cemented carbide substrate and themass of diamond particles is placed in the recess. After formation ofthe diamond compact, the sides of the substrate may be removed to exposethe diamond compact. The diamond synthesis conditions will typically bea pressure of 40 to 70 kilobars (4 to 7 GPa) and a temperature of 1300to 1600° C. These conditions will typically be maintained for a periodof 20 to 60 minutes.

An embodiment of the invention will now be described. A cylindricalcemented carbide substrate was provided. The substrate comprised a massof tungsten carbide particles bonded into a coherent form by means of anickel/cobalt alloy. The mass ratio of the nickel to cobalt in the alloywas 40:60.

A recess was formed in one flat end surface of the substrate. A mass ofdiamond particles was placed in the recess and filled the recess. Thisunbonded assembly was placed in the reaction zone of a conventional hightemperature/high pressure apparatus and subjected to a temperature ofabout 1500° C. and a pressure of about 55 kilobars (5,5 GPa). Theseconditions were maintained for a period sufficient to produce a diamondcompact of the diamond particles. During the formation of the compact,nickel/cobalt alloy from the substrate infiltrated the diamond mass andformed a second phase for the diamond compact. The diamond compact wasbonded to the cemented carbide body.

The resulting product was removed from the apparatus and the sides ofthe cemented carbide substrate removed. The resulting product isillustrated by the accompanying drawing and consisted of a diamondcompact 12 bonded to a cemented carbide substrate 10 along interface 14.The diamond compact 12 had a second phase consisting essentially of anickel/cobalt alloy and the cemented carbide substrate 10 had a binderconsisting essentially of the same alloy. The diamond compact 12 has anupper working surface 16 and a peripheral cutting edge 18.

The composite abrasive compact illustrated by the drawing may be used asa drill insert. In use, the cutting edge 18 performs a cutting action indrilling and in hard rocks temperatures in excess of 500° C. areencountered. Due to the presence of the nickel/cobalt alloy in both thediamond compact and in the cemented carbide substrate, the thermalfatigue resistance of the composite compact is increased and there isreduction in the tendency for snake skin cracking to occur, as is acommon problem with prior art composite compacts using cobalt as thebinder alloy.

1. A composite diamond compact comprising a diamond compact bonded to acemented carbide substrate, the diamond compact comprising apolycrystalline bonded mass of diamond crystals present in an amount ofat least 80 percent by volume of the diamond compact and a second phaseconsisting essentially of a nickel/cobalt alloy, the cemented carbidesubstrate comprising a mass of carbide particles bonded into a coherentform by means of a binder consisting essentially of a nickel/cobaltalloy.
 2. The composite diamond compact according to claim 1, whereinthe mass ratio of nickel to cobalt in both of the nickel/cobalt alloysis in the range 75:25 to 20:80.
 3. The composite diamond compactaccording to claim 1, wherein the mass ratio of nickel to cobalt in bothof the nickel/cobalt alloys is in the range 30:70 to 45:55.
 4. A Thecomposite diamond compact according to claim 1, wherein the mass ratioof nickel to cobalt in both of the nickel/cobalt alloys is 40:60.
 5. Thecomposite diamond compact according to claim 1, wherein the carbideparticles of the substrate are selected from tungsten carbide particles,tantalum carbide particles, titanium carbide particles, molybdenumcarbide particles and a mixture containing two or more of suchparticles. 6-7. (canceled)
 8. The composite diamond compact according toclaim 2, wherein the carbide particles of the substrate are selectedfrom tungsten carbide particles, tantalum carbide particles, titaniumcarbide particles, molybdenum carbide particles and a mixture containingtwo or more of such particles.
 9. The composite diamond compactaccording to claim 3, wherein the carbide particles of the substrate areselected from tungsten carbide particles, tantalum carbide particles,titanium carbide particles, molybdenum carbide particles and a mixturecontaining two or more of such particles.
 10. The composite diamondcompact according to claim 4, wherein the carbide particles of thesubstrate are selected from tungsten carbide particles, tantalum carbideparticles, titanium carbide particles, molybdenum carbide particles anda mixture containing two or more of such particles.
 11. A method forcutting comprising: cutting with a composite diamond compact, whereinthe composite diamond compact comprises a diamond compact bonded to acemented carbide substrate, the diamond compact comprising apolycrystalline bonded mass of diamond crystals present in an amount ofat least 80 percent by volume of the diamond compact and a second phaseconsisting essentially of a nickel/cobalt alloy, the cemented carbidesubstrate comprising a mass of carbide particles bonded into a coherentform by means of a binder consisting essentially of a nickel/cobaltalloy; and wherein said cutting is carried out at a temperature inexcess of 500° C. at a cutting edge of the composite diamond compact.12. The method according to claim 11, wherein the mass ratio of nickelto cobalt in both of the nickel/cobalt alloys is in the range 75:25 to20:80.
 13. The method according to claim 11, wherein the mass ratio ofnickel to cobalt in both of the nickel/cobalt alloys is in the range30:70 to 45:55.
 14. The method according to claim 11, wherein the massratio of nickel to cobalt in both of the nickel/cobalt alloys is 40:60.15. The method according to claim 11, wherein the carbide particles ofthe substrate are selected from tungsten carbide particles, tantalumcarbide particles, titanium carbide particles, molybdenum carbideparticles and a mixture containing two or more of such particles.